There is a case when hazardous substances, malodorous substances, and so on are contained in atmospheric gas in a life space, a refrigerator, a warehouse, and so on and exhaust gas from a process unit. A small-sized gas decomposition device (including an air cleaning device, an air cleaning air conditioner, and a gas purifying device) decomposing, sterilizing, and so on (hereinafter, to be referred to as gas decomposition) these hazardous substances, malodorous substances, and so on with high efficiency has been required.
Generally, in the gas decomposition device, decomposition object gas is introduced into a gas decomposition chamber by a blower, and is decomposed and purified by discharge, a decomposition catalyst, a photocatalyst, or radical (ozone and so on).
Besides, a technology in which process object gas is blown to a purification processing means by using a plasma actuator is also disclosed.
However, it is not necessarily easy in the gas decomposition device to decompose hardly decomposable gas at high speed.
In the gas decomposition device, improvement in a gas decomposition ratio means a process of a large gas flow rate and a large gas decomposition reaction rate. These are described below.
A) Large Flow Rate Process
A gas decomposition method by a catalyst is simple and easy, and frequently used. However, this method uses an adsorption and decomposition reaction of gas by a reaction at a catalyst surface. Accordingly, when a surface area is not enough large relative to a gas flow path, it becomes difficult to secure a reaction rate. At this time, a fine-meshed catalyst-carrying filter is used to increase the surface area. As a result, a pressure loss becomes large and it is difficult to enable a large flow rate. To overcome the pressure loss, a large amount of blowing is necessary to incur large-sizing of a device, increase in price, and increase in power consumption. Further, periodical exchange of filters become necessary to resolve clogging.
In case of the photocatalyst, a reaction occurs only at a surface where light is irradiated, and therefore, both an arrival of the decomposition object gas to the surface and the light irradiation are required, and it is difficult to enlarge decomposition efficiency. Besides, a large surface area to enable the above becomes necessary, and the device becomes large.
The gas decomposition by discharge uses a decomposition reaction in a gas phase. However, a discharge range in an atmospheric pressure, for example, a discharge range of a needle electrode is very small such as approximately 1 mm or less of a tip part of the needle. Accordingly, it is necessary to densely dispose an electrode group to avoid undecomposition caused by passing over of gas. As a result, the pressure loss becomes large, and a large-capacity and large-sized blower becomes necessary to enable the large flow rate.
Namely, in a general gas decomposition device, the gas decomposition ratio and the pressure loss are in a trade-off relationship. Therefore, a large-sized device becomes necessary to enable the large flow rate of gas decomposition process. Namely, a small-sizing of the device becomes difficult, and the exchange of filter becomes necessary.
B) Large Gas Decomposition Reaction Rate
The gas decomposition reaction rate is determined by an amount of chemical species which causes the decomposition and a reaction rate (when the gas decomposition is performed by an oxidation reaction, an amount of oxidant and an oxidation reaction rate (oxidation potential)). Ozone is easy to be generated by discharge, a high density supply is possible, in addition, a lifetime is long, and therefore, it is often used for the gas decomposition process. Ozone is effective for decomposition of ammonia and formaldehyde gas. However, ozone is in short of an oxidizing power for decomposition of hardly decomposable gas (for example, toluene and acetaldehyde gas). Therefore, it is difficult to decompose the hardly decomposable gas at high speed even if ozone is supplied in high concentration.
OH radical, O radical having active oxygen have much stronger oxidizing power, and are able to decompose the hardly decomposable gas at high speed. However, reactivities of OH radical and O radical are high, and therefore, lifetimes thereof are short, and it is difficult to supply them in high density to the decomposition object gas.
There is a method in which a reactant is held at a filter, a mesh, and so on to increase the chemical species incurring the decomposition. However, diffusion and supply of the object gas to the surface is also necessary in this method, and as a result, it is difficult to enable approximation and reaction of the oxidant and the object gas in bulk.